1,153 research outputs found
Test of asymptotic freedom and scaling hypothesis in the 2d O(3) sigma model
The 7--particle form factors of the fundamental spin field of the O(3)
nonlinear --model are constructed. We calculate the corresponding
contribution to the spin--spin correlation function, and compare with
predictions from the spectral density scaling hypothesis. The resulting
approximation to the spin--spin correlation function agrees well with that
computed in renormalized (asymptotically free) perturbation theory in the
expected energy range. Further we observe simple lower and upper bounds for the
sum of the absolute square of the form factors which may be of use for analytic
estimates.Comment: 14 pages, 3 figures, late
Quantum corrections of Abelian Duality Transformations
A modification of the Abelian Duality transformations is proposed
guaranteeing that a (not necessarily conformally invariant) -model be
quantum equivalent (at least up to two loops in perturbation theory) to its
dual. This requires a somewhat non standard perturbative treatment of the {\sl
dual} -model. Explicit formulae of the modified duality transformation
are presented for a special class of block diagonal purely metric
-models.Comment: Latex 11 pages; remarks on a free model and references adde
Coadjoint orbits of the Virasoro algebra and the global Liouville equation
The classification of the coadjoint orbits of the Virasoro algebra is
reviewed and is then applied to analyze the so-called global Liouville
equation. The review is self-contained, elementary and is tailor-made for the
application. It is well-known that the Liouville equation for a smooth, real
field under periodic boundary condition is a reduction of the SL(2,R)
WZNW model on the cylinder, where the WZNW field g in SL(2,R) is restricted to
be Gauss decomposable. If one drops this restriction, the Hamiltonian reduction
yields, for the field where is a constant,
what we call the global Liouville equation. Corresponding to the winding number
of the SL(2,R) WZNW model there is a topological invariant in the reduced
theory, given by the number of zeros of Q over a period. By the substitution
, the Liouville theory for a smooth is recovered in
the trivial topological sector. The nontrivial topological sectors can be
viewed as singular sectors of the Liouville theory that contain blowing-up
solutions in terms of . Since the global Liouville equation is
conformally invariant, its solutions can be described by explicitly listing
those solutions for which the stress-energy tensor belongs to a set of
representatives of the Virasoro coadjoint orbits chosen by convention. This
direct method permits to study the `coadjoint orbit content' of the topological
sectors as well as the behaviour of the energy in the sectors. The analysis
confirms that the trivial topological sector contains special orbits with
hyperbolic monodromy and shows that the energy is bounded from below in this
sector only.Comment: Plain TEX, 48 pages, final version to appear in IJMP
Discrete Symmetry Enhancement in Nonabelian Models and the Existence of Asymptotic Freedom
We study the universality between a discrete spin model with icosahedral
symmetry and the O(3) model in two dimensions. For this purpose we study
numerically the renormalized two-point functions of the spin field and the four
point coupling constant. We find that those quantities seem to have the same
continuum limits in the two models. This has far reaching consequences, because
the icosahedron model is not asymptotically free in the sense that the coupling
constant proposed by L"uscher, Weisz and Wolff [1] does not approach zero in
the short distance limit. By universality this then also applies to the O(3)
model, contrary to the predictions of perturbation theory.Comment: 18 pages, 8 figures Color coding in Fig. 5 changed to improve
visibilit
Equilibriumlike invaded cluster algorithm: critical exponents and dynamical properties
We present a detailed study of the Equilibriumlike invaded cluster algorithm
(EIC), recently proposed as an extension of the invaded cluster (IC) algorithm,
designed to drive the system to criticality while still preserving the
equilibrium ensemble. We perform extensive simulations on two special cases of
the Potts model and examine the precision of critical exponents by including
the leading corrections. We show that both thermal and magnetic critical
exponents can be obtained with high accuracy compared to the best available
results. The choice of the auxiliary parameters of the algorithm is discussed
in context of dynamical properties. We also discuss the relation to the
Li-Sokal bound for the dynamical exponent .Comment: 11 pages, 13 figures, accepted for publication in Phys. Rev.
Toward an understanding of short distance repulsions among baryons in QCD -- NBS wave functions and operator product expansion --
We report on our recent attempts to determine the short distance behaviors of
general 2-baryon and 3-baryon forces, which are defined from the
Nambu-Bethe-Salpeter(NBS) wave function, by using the operator product
expansion and a renormalization group analysis in QCD. We have found that the
repulsion at short distance increases as the number of valence quarks increases
or when the number of different flavors involved decreases. This global
tendency suggests a Pauli suppression principle among quark fields at work.Comment: 14 pages, add two exmples in sect.3.4, a version accepted for
Progress of Theoretical Physic
Photocount statistics in mesoscopic optics
We report the first observation of the impact of mesoscopic fluctuations on
the photocount statistics of coherent light scattered in a random medium.
Poisson photocount distribution of the incident light widens and gains
additional asymmetry upon transmission through a suspension of small dielectric
spheres. The effect is only appreciable when the average number of
photocounts becomes comparable or larger than the effective dimensionless
conductance g of the sample.Comment: Thoroughly revised text and figures, new data set, new figure adde
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